SearchStorage asks questions in part one of its virtualization MegaFAQ, and discusses five general virtualization frequently asked questions:
Q: What is storage virtualisation? Why do I need it? What does it buy me?
A: There's a significant amount of confusion in the market. In general, we've seen a lot of interest and excitement in the server virtualisation world, and now that same kind of enthusiasm is appearing in the storage virtualisation side.
Today's data centre is made up of many large independent systems. That is, you have a server, there is some storage attached to it, the server has an operating system (e.g., Windows, Linux, Solaris, etc.), and it runs a particular application. That stack [of hardware and software] is its own "silo," and you can have hundreds and sometimes thousands of these silos in the data centre of today's larger enterprises. This proliferation has made management very difficult.
The solution to this complexity is to provide a layer of virtualisation at the server level, which is being done with products like Xensource or VMware or Microsoft Virtualisation Server. Then, you have virtualisation applied at the networking layer and virtualisation available at the storage layer. The goal is to virtualise the entire data centre environment over the next two or three years so that a "utility capability" becomes available, eliminating these silos so that managing the overall environment becomes easier, and we start getting applications delivered as if they were a utility at a level of performance that the users have requested.
With that backdrop in mind, let's focus on storage virtualisation. Think of it as an abstraction layer put on top of a large number of physical storage devices. We have a massive proliferation of physical storage devices and arrays and JBODs all over the enterprise (not only in the data centre). Managing these storage boxes has become literally impossible. The abstraction possible with storage virtualisation "hides" the idiosyncrasies of each physical storage system and provides a common way of dealing with all of these disparate devices, significantly easing storage management.
Storage virtualisation also provides a consistent interface for all storage applications. In other words, a storage array today from IBM, EMC, Hitachi Data Systems (HDS) or other vendors comes with its own set of storage applications like replication, mirroring, snapshots, etc., but the actual applications are different for each system. By adding storage virtualisation on top of these heterogeneous boxes, you enable a single set of storage applications so there's no need to learn multiple applications to achieve the same function. This is also true for tasks like data migration and consolidation, and makes these otherwise disruptive tasks far less disruptive to the storage enterprise.
Suppose you wanted to change RAID protection from RAID-0 to RAID-5. Today, you'd have to backup the data, create another RAID 5 LUN and then bring the data back onto the new LUN. It's a very disruptive process. If you want to create tiered storage, you'd probably have two or three separate storage boxes as Tier 1, Tier 2 and Tier 3 -- you can't bring those boxes together. Storage virtualisation eliminates both of these problems and enables replication between heterogeneous boxes.
Q: Who offers storage virtualisation? What are the differences?
A: There are numerous players in the storage virtualisation market today, but I can categorise them as in-band vendors (typically appliances), out-of-band vendors and Split Path Architecture for Intelligent Devices (SPAID) vendors.
For the in-band category, we have companies like IBM with its Storage Virtualisation Controller (SVC) product, DataCore Software with its SANsymphony, FalconStor Software with its IPStor. Those are three good examples of what companies are in the game, and all three are seasoned players with storage virtualisation product offerings for between three and five years.
StoreAge, which was recently acquired by LSI, has essentially been the only out-of-band product in the industry. The Storage Virtualisation Manager (SVM) product runs on its own Intel server-based appliance. It has also recently ported that software to purpose-built appliances from QLogic and Emulex.
The SPAID category of products includes products like Network Storage Platform (NSP) from Incipient and Invista from EMC. These are similar to an out-of-band architecture, but both are designed to utilise an intelligent switch in the network environment. For example, both Incipient NSP and EMC Invista work with Cisco Systems/Brocade Communications Systems intelligent switches.
HDS represents a small fourth category of storage virtualisation where the feature is actually implemented within the storage cabinet itself. The TagmaStore system is one good example of this approach.
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